This invention relates to a method and an apparatus for detecting and inserting an electronic watermark in a digital image according to a MPEG (Moving Picture Experts Group) standard and, in particular, to a method of adjusting the insertion intensity of an electronic watermark.
Japanese Unexamined Patent Publication No. H11-55638 discloses an information adding (or superimposing) device for adding information to an image by selecting at least a partial area within the image as an information adding area and enlarging or reducing the image in the information adding area. Thus, the above-mentioned Japanese Unexamined Patent Publication No. H11-55638 describes an electronic watermark insertion algorithm for inserting an electronic watermark by enlarging or reducing the image. However, the above-mentioned Japanese Unexamined Patent Publication No. H11-55638 does not describe the adjustment of the insertion intensity of the electronic watermark.
Japanese Unexamined Patent Publication No. H11-98341 discloses another electronic watermark insertion algorithm for inserting an electronic watermark into a quantized DCT (Discrete Cosine Transform) coefficient at random. However, the above-mentioned Japanese Unexamined Patent Publication No. H11-98341 does not describe the adjustment of the insertion intensity of the electronic watermark.
Japanese Unexamined Patent Publication No. H11-212463 discloses another electronic watermark insertion algorithm for inserting an electronic watermark after one-dimensional data such as a speech sound is subjected to modified discrete cosine transform (modified DCT). However, the abovementioned Japanese Unexamined Patent Publication No. H11-212463 does not describe the adjustment of the insertion intensity of the electronic watermark.
Thus, all of the three publications mentioned above relate to the electronic watermark insertion algorithm itself while this invention relates to the adjustment of the insertion intensity of the electronic watermark.
In recent years, a digital image is easily sent to a user by the spread of digital satellite broadcasting, internetworking distribution, a DVD (Digital Video or Versatile Disc), and so on. The digital image is not deteriorated in quality even if it is duplicated or reproduced. Therefore, copyright protection of the digital image is an important problem. In order to realize the copyright protection, proposal is made of a technique of adding copyright information as an electronic watermark in a DCT (Discrete Cosine Transform) coefficient region of the digital image.
Referring to FIG. 1, a related electronic watermark detecting/inserting device serves as an information inserting device in a DCT coefficient. The electronic watermark is a technique intended for the copyright protection and has a function of managing generation information. When an input digital image comprising a first electronic watermark inserted therein is supplied as an MPEG stream, the electronic watermark detecting/inserting device produces an output digital image containing a second electronic watermark inserted therein subsequently to the first electronic watermark. Specifically, if the second electronic watermark is not detected from the input digital image after the first electronic watermark is detected from the input digital image, the electronic watermark detecting/inserting device produces the output digital image containing the second electronic watermark inserted therein subsequently to the first electronic watermark.
The electronic watermark detecting/inserting device comprises a preprocessing section 10′ for receiving, as a digital image to be subjected to electronic watermark insertion, image data (MPEG stream) encoded by the MPEG standard. The preprocessing section 10′ carries out an operation similar to ordinary MPEG decoding upon the MPEG stream as the image data. The ordinary MPEG decoding comprises four major operations including header search, VLD (Variable Length Decoding), quantization, and IDCT (Inverse Discrete Cosine Transform). On the other hand, the preprocessing section 10′ of the electronic watermark detecting/inserting device illustrated in FIG. 1 does not carry out the IDCT. The preprocessing section 10′ produces data (header data) other than a block layer, a run and a level (which will later be described) produced by the VLD of the data of the block layer, and a DCT coefficient. The DCT coefficient is obtained by multiplying the level and a quantization coefficient. The quantization coefficient is obtained by multiplying a quantization scale and a quantization table.
In FIG. 1, an electronic watermark detecting section 30′ can detect both of the first and the second electronic watermarks and, if the second electronic watermark is not detected after the first electronic watermark is detected, sends a request for insertion of the second electronic watermark to an electronic watermark inserting section 20′. Supplied from the electronic watermark detecting section 30′ with the request for insertion of the second electronic watermark, the electronic watermark inserting section 20′ inserts the second electronic watermark.
Description will be made in detail about the operation of the electronic watermark detecting/inserting device illustrated in FIG. 1.
The electronic watermark detecting section 30′ is supplied from the preprocessing section 10′ with the DCT coefficient and carries out a detecting operation for the first electronic watermark. If the first electronic watermark is detected as a result of detection, another detecting operation for the second electronic watermark is carried out. If the second electronic watermark is not detected, the electronic watermark detecting section 30′ judges that the second electronic watermark must be inserted into the image data in consideration, and supplies the electronic watermark inserting section 20′ with a request for insertion of the second electronic watermark.
In response to the request, the electronic watermark inserting section 20′ inserts the second electronic watermark. At this time, the electronic watermark inserting section 20′ is supplied from the preprocessing section 10′ with the run and the level and inserts the second electronic watermark into the image data.
A VLC/MUX section 60′ carries out VLC (Variable Length Coding) upon the level and the run produced by the electronic watermark inserting section 20′ to produce coded data of the block layer in the MPEG stream. The VLC/MUX section 60 carries out MUX (multiplexing) for the coded data and the header data separated by the preprocessing section 10′ to reproduce the MPEG stream.
Thus, the electronic watermark detecting section 30′ is supplied from the preprocessing section 10′ with the DCT coefficient and detects the first electronic watermark and the second electronic watermark following thereto. If the second electronic watermark is not detected after the first electronic watermark is detected, the electronic watermark detecting section 30′ supplies the electronic watermark inserting section 20′ with the request for insertion of the second electronic watermark. In response to the request, the electronic watermark inserting section 20′ is supplied with the run and the level from the preprocessing section 10′ and inserts the second electronic watermark into the image data. Once the insertion of the second electronic watermark is started, the electronic watermark inserting section 20′ inserts the second electronic watermark of a predetermined intensity unless a request for stopping the insertion is received.
In the electronic watermark inserting method of the above-mentioned structure, the electronic watermark of the predetermined intensity is inserted into either of the image data weak in detection intensity of the second electronic watermark and the image data strong in detection intensity.